This invention relates to a novel workpiece having a machine-readable marking abraded into a surface thereof and to a novel method for producing such markings in the workpiece.
As an aid to manufacturing operations, it may be desirable to provide a unique marking on each workpiece that is processed. Such a marking can be used as part of the control system in automated manufacturing processes, Also, such a marking can be used for the computerized accumulation of historical data about the workpiece, which may later be used for quality control and for warranty purposes.
Such markings have been suggested before, but none have had all of the characteristics that are desirable, and which, in the present competitive marketplace, are necessary, for practical commercial use. Such markings, for example, must be capable of being produced by machine on each workpiece on demand at low cost, and also must be machine-readable with high reliability also at low cost. Because the workpiece is still in process, the marking must be resistant to degradation when exposed to temperatures up to at least 450.degree. C. and to chemical attack during the processing of the workpiece. Also, the marking must be capable of being produced on flat or nonflat surfaces.
Some prior systems of marking, usually implemented by applying labels to finished articles, employed a bar-code. A bar-code marking, which is machine readable, comprises a related sequence of substantially parallel bars of predetermined widths and spacings. Bar-code markings can be printed before demand or on demand with commercially-available printers, and the markings can be read with commercially-available readers. However, using labels with bar-coded markings on in-process workpieces has been found to be unsatisfactory, particularly on glass workpieces. Not only may the marking be degraded by the processing of the workpiece, but also the label itself and the substance used to attach the label to the workpiece may be degraded by the processing of the workpiece.